Design and operation of a UHV double-bounce harmonic rejection mirror for XAFS studies

A simple but effective harmonic rejection system has been installed on beamline X-11B at the NSLS. The system includes a parallel pair of nickel-coated float glass mirrors. This geometry allows an output beam whose direction is independent of the incidence angle on the mirrors. They are housed within a UHV chamber and situated 2.0 m upstream of the sample position and 8 m downstream of a double crystal monochromator. The angle of the mirror pair is adjusted by a single stepper motor. In its current configuration the double-bounce system works for energies between about 2 and 6 keV. For harmonic rejection of energies higher than this, the whole device may be repositioned to permit a single bounce of the x-ray beam from one of the mirrors. The features and operation of this simple device are discussed.